1. Technical Field
The present invention relates to a method of fabricating an analog capacitor, and more particularly, to a method of fabricating an analog capacitor using a post-treatment technique.
2. Discussion of the Related Art
An analog capacitor is a unit element that is commonly used in an analog to digital (AD) converter, an RF device, a switching capacitor filter, a CMOS image sensor, or the like. The analog capacitor stores information in analog form, and has the property that the quantity of stored electric charge is varied, depending on the applied voltage.
Further, it is preferable that such an analog capacitor should demonstrate the properties of a low voltage coefficient of capacitance (VCC) and a low leakage current. The VCC required is a small level in its absolute value. Hereinafter, the value of the VCC refers to a dimension of its absolute value. In order to improve the VCC property, a capacitor having a poly-insulator-poly (PIP) structure has been replaced with an analog capacitor having a metal-insulator-metal (MIM) structure. However, such a capacitor having the MIM structure still exhibits a relatively high VCC.
Therefore, efforts have been made toward post-treating the bottom electrode and the dielectric layer of the capacitor in order to reduce the leakage current of the capacitor. A method of post-treating the lower electrode and/or the capacitor dielectric layer is disclosed in U.S. Pat. No. 6,143,598 entitled “Method of fabrication of low leakage capacitor” to Martin, et al., and also, in U.S. Pat. No. 6,103,567 entitled “Method of fabricating dielectric layer” to Shih, et al.
The method disclosed by Martin, et al. includes depositing a first electrode of a capacitor. The first electrode is plasma-treated in an oxidizing medium where nitrogen and oxygen are present. Then, a dielectric layer is deposited, and the dielectric layer is plasma-treated in an oxidizing medium where nitrogen and oxygen are present. Then, a top electrode of a capacitor is formed. Further, dinitrogen oxide (N2O) may be used to plasma-treat the electrode. In the meantime, the method disclosed by Shih, et al. includes forming a high-k dielectric layer such as a tantalum oxide layer (Ta2O5), and performing a plasma-treatment or a deep ultra-violet ozone treatment.
According to these methods, the dielectric layer is post-treated in an oxidizing medium where nitrogen and oxygen are present, or treated with oxygen plasma or ozone, thereby reducing a leakage current. However, the methods do not achieve a reduction in the VCC property of the analog capacitor.